Such a power-assisted wheelchair is situated between the manual wheelchair and the motor-operated wheelchair. The human power applied intermittently to the paired right and left wheels is detected, and assist power commensurate with the detected human power is added respectively to the right and left wheels to alleviate the physical effort of the rider.
Here, with this kind of power-assisted wheelchair, the assist power is supplied intermittently every time the human power applied to each wheel is detected. After the human power is removed, the assist power is caused to attenuate with the lapse of time to provide the wheelchair rider with a coasting impression (Refer to the JP(A) Hei-8-168506).
However, the conventional power-assisted wheelchair so far has had problems: the time-attenuation rate of the assist power is set to be always constant irrespective of the magnitude of the human power and the running speed or the running direction (forward or reverse). As a result, on a road surface having a small running resistance, the running continues more than expected when the coasting amount is too great for example, and the turning radius cannot be made small for the small indoor movements. When the coasting amount is insufficient on the contrary, running is not easy on the road having a large running resistance or on a steep slope.
Also there are cases in which, when the wheelchair negotiates a step or the like, the wheelchair ends up in coasting farther than expected.
Furthermore, coasting of the wheelchair in the reverse direction causes unnecessary impression of fear to the rider. When the coasting amount is insufficient on the contrary, even if human power is applied to the wheels in the reverse direction or to counter the wheel rotation on a steep downhill for example with the intention of producing brake forces, stabilized brake forces may not be produced.
Therefore, the object of this invention is to provide a power-assisted wheelchair capable of making small radius indoor running, comfortable outdoor running, easy uphill running, stabilized downhill running, and eliminating the impression of fear during a reverse running.